The present invention relates to an abrasive composition for substrates of magnetic recording media which provides an abraded surface with a low surface roughness at an improved rate of abrasion. The present invention also relates to a process for producing substrates of magnetic recording media using the abrasive composition, particularly a process for producing substrates of magnetic recording media using Nixe2x80x94P plated aluminum alloy substrates and carbon substrates.
Abrasive compositions comprising abrasive particles and an aliphatic organic sulfate, an oxyalkylene alkyl ether sulfate or an ampholytic surface active agent are disclosed, e.g., in Japanese Patent Laid-Open Nos. 51-16308 (corresponding to U.S. Pat. No. 3,985,668), 51-76685 (corresponding to U.S. Pat. No. 4,051,056), 62-43482, 2-73898, 4-291723, 5-230440 and 8-41443.
Of the known abrasive compositions the one described in Japanese Patent Laid-Open Nos. 51-16308 and 51-76685 are detergents for a hard surface for domestic use simply called cleansers.
Japanese Patent Laid-Open No. 2-73898 also discloses a cleanser, aiming at preventing abrasive particles from precipitating with lapse of time during long-term storage (improving suspension stability) and improving flowability. The abrasive particles used in the composition are not sufficiently hard. Therefore, rate of abrading substrates of magnetic recording media cannot be improved, and a low surface roughness of the substrates cannot be achieved with this composition.
The abrasive composition described in Japanese Patent Laid-Open No. 62-43482 was developed with the intention of preventing abrasive particles from pricipitating with lapse of time and improving wetting properties and spreadability to the materials to be abraded. Rate of abrading substrates of magnetic recording media cannot be improved, and a low surface roughness of substrates cannot be achieved with this composition.
The abrasive composition described in Japanese Patent Laid-Open No. 4-291723 relates to the abrasion for silicon wafer, aiming at preventing clouds on surfaces of a silicon wafer. There is nothing to disclose to improve the rate of abrading substrates of magnetic recording media and to achieve a low surface roughness of substrates.
The abrasive composition described in Japanese Patent Laid-Open No. 5-230440 relates to the abrasion using diamond, aiming at preventing substrate surfaces from the damage caused by the contact of the work and abrasive particles left between the work and platen. There is nothing to disclose to improve the rate of abrading substrates of magnetic recording media, and to achieve a low surface roughness of substrates.
The abrasive composition described in Japanese Laid-Open No. 8-41443 is used in combination with an abrading buff, aiming at enhancing the surface luster of stainless steel or non-iron metal to give appliances or interior decoration a good appearance. There is nothing to disclose to improve the rate of abrading substrates of magnetic recording media and to achieve a low surface roughness of substrates.
Abrasive compositions comprising abrasive particles, such as diamond, alumina or SiC, of submicrons or several tens of microns in size dispersed in water, which are used for surface abrasion of brittle materials such as glass materials, carbon substrates and ceramic materials, and ductile materials such as Nixe2x80x94P plated aluminum are also known (see Japanese Patent Laid-Open Nos. 54-89389, 1-205973, 1-97560 and 9-143455) as other related art.
However, these conventional abrasive compositions were unsatisfactory in dispersibility of abrasive particles, dispersibility and removability of the waste chips or powders resulting from abrasion, and prevention of re-adhesion of the waste chips or powders, which tends to cause surface defects, such as pits or scratches. Further, the rate of abrasion cannot be raised, imposing a limit on cost reduction.
Accordingly, an object of the present invention is to provide an abrasive composition for substrates of magnetic recording media which can provide an abraded surface with a low roughness at an improved rate of abrasion without causing surface defects such as pits and scratches.
Another object of the present invention is to provide an abrasive composition for substrates of magnetic recording media suitable for abrading brittle materials such as glass, carbon and ceramics.
A further object of the present invention is to provide an abrasive composition for substrates of magnetic recording media suitable for abrading ductile materials such as Al, Si, W and Cu metals, particularly abrading Nixe2x80x94P plated aluminum alloy substrates.
A still further object of the present invention is to provide an abrasive composition suitable for abrading substrates of magnetic recording media, particularly abrading substrates for hard disks.
A still further object of the present invention is to provide a process for producing substrates of magnetic recording media free from pits or scratches.
As a result of extensive investigations, the inventors of the present invention have found that the above objects can be accomplished by an abrasive composition for substrates of magnetic recording media which contains a specific abrasive auxiliary and is adjusted to have a pH within a specific range, and a process for producing substrates of magnetic recording media using the abrasive composition.
The present invention has been completed based on this finding. That is, the above objects have been achieved by an abrasive composition for substrates of magnetic recording media, containing at least an abrasive, an abrasive auxiliary and water, wherein the abrasive auxiliary comprises at least one aliphatic organic sulfate, and the composition has a pH of 1 to 13.
Further, the above objects have been achieved by an abrasive composition for substrates of magnetic recording media, containing at least an abrasive, an abrasive auxiliary and water, wherein the abrasive auxiliary comprises at least one oxyalkylene alkyl ether sulfate represented by formula (2), and the composition has a pH of 1 to 13.
Rxe2x80x94Oxe2x80x94(AO)nxe2x80x94SO3Mxe2x80x83xe2x80x83(2)
wherein R represents a straight-chain or branched alkyl group, an aryl group or an alkylaryl group each having 5 to 21 carbon atoms; AO represents an oxyalkylene group having 2 or 3 carbon atoms; n represents a natural number of 1 to 30; and M represents an alkali metal, an alkaline earth metal or an organic cation.
Furthermore, the above objects have been achieved by an abrasive composition for substrates of magnetic recording media, containing at least an abrasive, an abrasive auxiliary and water, wherein the abrasive auxiliary comprises at least one amphoteric surface active agent, and the composition has a pH of 1 to 13.
The present invention also provides a process for producing substrates of magnetic recording media, comprising the step of abrading a substrate precursor with an abrasive composition containing at least an abrasive, an abrasive auxiliary and water, wherein the above-described abrasive compositions for substrates of magnetic recording media are used.